On Tue, 15 Apr 2025 at 15:10, Thomas Weißschuh <thomas.weisssc...@linutronix.de> wrote: > > Not all tasks have an ABI associated or vDSO mapped, > for example kthreads never do. > If such a task ever ends up calling stack_top(), it will derefence the > NULL ABI pointer and crash. > > This can for example happen when using kunit: > > mips_stack_top+0x28/0xc0 > arch_pick_mmap_layout+0x190/0x220 > kunit_vm_mmap_init+0xf8/0x138 > __kunit_add_resource+0x40/0xa8 > kunit_vm_mmap+0x88/0xd8 > usercopy_test_init+0xb8/0x240 > kunit_try_run_case+0x5c/0x1a8 > kunit_generic_run_threadfn_adapter+0x28/0x50 > kthread+0x118/0x240 > ret_from_kernel_thread+0x14/0x1c > > Only dereference the ABI point if it is set. > > Also move the randomization adjustment into the same conditional. > > Signed-off-by: Thomas Weißschuh <thomas.weisssc...@linutronix.de> > ---
This looks good to me -- we've hit what's effectively the same issue
on other architectures with this test, with similar resolutions.
Reviewed-by: David Gow <david...@google.com>
I'm happy to have this (and the following path) go in via the KUnit
tree, but if you'd rather have it go via MIPS, that's fine, too. (The
qemu_configs won't generate any merge conflicts.)
-- David
> arch/mips/kernel/process.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> index
> b630604c577f9ff3f2493b0f254363e499c8318c..02aa6a04a21da437909eeac4f149155cc298f5b5
> 100644
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -690,18 +690,20 @@ unsigned long mips_stack_top(void)
> }
>
> /* Space for the VDSO, data page & GIC user page */
> - top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> - top -= PAGE_SIZE;
> - top -= mips_gic_present() ? PAGE_SIZE : 0;
> + if (current->thread.abi) {
> + top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> + top -= PAGE_SIZE;
> + top -= mips_gic_present() ? PAGE_SIZE : 0;
> +
> + /* Space to randomize the VDSO base */
> + if (current->flags & PF_RANDOMIZE)
> + top -= VDSO_RANDOMIZE_SIZE;
> + }
>
> /* Space for cache colour alignment */
> if (cpu_has_dc_aliases)
> top -= shm_align_mask + 1;
>
> - /* Space to randomize the VDSO base */
> - if (current->flags & PF_RANDOMIZE)
> - top -= VDSO_RANDOMIZE_SIZE;
> -
> return top;
> }
>
>
> --
> 2.49.0
>
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